U.S. patent application number 11/119365 was filed with the patent office on 2006-11-02 for circuit protection device.
Invention is credited to Gregory P. Aszmus.
Application Number | 20060245125 11/119365 |
Document ID | / |
Family ID | 36950498 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060245125 |
Kind Code |
A1 |
Aszmus; Gregory P. |
November 2, 2006 |
Circuit protection device
Abstract
A circuit protection device including a conductor arm releasably
connected between a voltage sensitive device and a circuit to be
protected. The connector arm is biased to move in a direction
generally parallel with a plane defined by a lateral dissection
between the releasably connected conductor arm and the voltage
sensitive device.
Inventors: |
Aszmus; Gregory P.; (Salt
Lake City, UT) |
Correspondence
Address: |
FACTOR & LAKE, LTD
1327 W. WASHINGTON BLVD.
SUITE 5G/H
CHICAGO
IL
60607
US
|
Family ID: |
36950498 |
Appl. No.: |
11/119365 |
Filed: |
April 30, 2005 |
Current U.S.
Class: |
361/56 |
Current CPC
Class: |
H01C 7/126 20130101 |
Class at
Publication: |
361/056 |
International
Class: |
H02H 9/00 20060101
H02H009/00 |
Claims
1. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; and, a thermal connector releasably connecting
the attachment surface of the second terminal of the voltage
sensitive element to the attachment surface of the conductor arm,
the conductor arm being biased to move, when released by the
thermal connector, in a direction along a line having an acute
angle with respect to a plane defined by a lateral dissection
between the connected attachment surfaces, the angle being no
greater than 45.degree. on either side of the plane.
2. The circuit protection device of claim 1 wherein the angle of
movement is approximately between 0.degree. and 10.degree., but
more optimally between 0.degree. and 5.degree., on either side of
the plane.
3. The circuit protection device of claim 1 further comprising: a
spring directly connected between the conductor arm and a support
structure, the spring biasing the conductor arm to move the
conductor arm upon release of the conductor arm from the voltage
sensitive element.
4. The circuit protection device of claim 3 wherein the spring is
in axial tension when the conductor arm is connected to the second
terminal and retracts to move the conductor arm upon its release
from the second terminal of the voltage sensitive device.
5. The circuit protection device of claim 3 wherein the spring is
in torsional stress when the conductor arm is connected to the
second terminal and relaxes the stress to move the conductor arm
upon its release from the second terminal.
6. The circuit protection device of claim 3 wherein the spring is
in axial compression when the conductor arm is connected to the
second terminal and axially extends to move the conductor arm upon
its release from the second terminal.
7. The circuit protection device of claim 1 wherein the voltage
sensitive element is a varistor.
8. The circuit protection device of claim 7 wherein the varistor is
a metal oxide varistor.
9. The circuit protection device of claim 1 wherein the thermal
connector is a low-temperature solder.
10. The circuit protection device of claim 9 wherein the
low-temperature solder liquefies at a temperature between
114-124.degree. C.
11. The circuit protection device of claim 1 further comprising: a
second voltage sensitive element having a first terminal and a
second terminal, the second terminal of the second voltage
sensitive element having an attachment surface; a second conductor
arm having an attachment surface; and, a second thermal connector
releasably connecting the attachment surface of the second terminal
of the second voltage sensitive element to the attachment surface
of the second conductor arm, the second connector arm being biased
to move in a direction generally parallel with a second plane
defined by a second lateral dissection between the connected
attachment surfaces of the second voltage sensitive element and the
second conductor arm.
12. The circuit protection device of claim 11 wherein both voltage
sensitive elements are connected together by a connecting structure
such that their respective conductor arms are contained in a space
defined between both voltage sensitive elements.
13. The circuit protection device of claim 12 wherein the
connecting structure is situated in a housing at least partially
surrounding the voltage sensitive devices.
14. The circuit protection device of claim 12 wherein the
connecting structure includes a first common terminal for
conductively coupling the first terminals of the voltage sensitive
devices.
15. The circuit protection device of claim 14 wherein the
connecting structure includes a second common terminal for
conductively coupling the conducting arms.
16. The circuit protection device of claim 1 including a braided
conductor connected between the conductor arm and a remote third
terminal adapted for connection to a circuit to be protected.
17. The circuit protection device of claim 16 including braided
conductors connecting between the conductor arms and the second
common terminal.
18. The circuit protection device of claim 1 wherein the conductor
arm is substantially flat with opposing relatively wider flat
surfaces relative to opposing relatively narrower edge surfaces, at
least one of the wider surfaces being oriented to face the voltage
sensitive device.
19. The circuit protection device of claim 1 wherein the voltage
sensitive device is an MOV and at least the second terminal is in
direct contact with a semiconductor core of the MOV.
20. The circuit protection device of claim 1 further comprising: a
non-conductive material substantially encasing the voltage
sensitive element wherein a portion of the second terminal remains
exposed; and, a conductive contact coupled to the exposed portion
of the second terminal, the conductive contact is positioned to
extend a distance beyond the non-conductive material with respect
to the plane.
21. The circuit protection device of claim 20 further comprising: a
sheet of dielectric material having an opening, the sheet being
disposed such that a portion of the sheet is between the voltage
sensitive element and the conductive contact and such that the
opening is adjacent and aligned with the exposed portion of the
second terminal.
22. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; and, a thermal connector releasably connecting
the attachment surface of the second terminal of the voltage
sensitive element to the attachment surface of the conductor arm,
the conductor arm being biased by a spring held in torsional
stress, the spring as it relaxes moving the conductor arm away from
the second terminal of the voltage sensitive device upon release of
the thermal connector.
23. The circuit protection device of claim 22 wherein the conductor
arm moves when released by the thermal connector, in a direction
along a line having an angle with respect to a plane defined by a
lateral dissection between the connected attachment surfaces, the
angle being no greater than 45.degree. on either side of the
plane.
24. The circuit protection device of claim 22 wherein the spring is
connected directly between the conductor arm and a support
structure.
25. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; a spring connected directly between the
conductor arm and a support structure; and, a thermal connector
releasably connecting the attachment surface of the second terminal
of the voltage sensitive element to the attachment surface of the
conductor arm, the conductor arm being biased by a spring held in
tension, the spring as it relaxes moving the conductor arm away
from the second terminal of the voltage sensitive device upon
release of the thermal connector.
26. The circuit protection device of claim 25 wherein the conductor
arm moves when released by the thermal connector, in a direction
along a line having an acute angle with respect to a plane defined
by a lateral dissection between the connected attachment surfaces,
the angle being no greater than 45.degree. on either side of the
plane.
27. The circuit protection device of claim 25 wherein the support
structure includes a mechanical coupler for an end of the spring,
the coupler being part of a remote terminal assembly electrically
connected to the conductive arm.
28. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; a thermal connector releasably connecting the
attachment surface of the second terminal of the voltage sensitive
element to the attachment surface of the conductor arm, the
conductor arm being biased by a spring to move the conductor arm
away from the second terminal of the voltage sensitive device upon
release of the thermal connector; and, a flexible conductor in the
form of a braided or twisted wire bundle connected between the
conductor arm and a remote terminal of the circuit protection
device.
29. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; and, a thermal connector releasably connecting
the attachment surface of the second terminal of the voltage
sensitive element to the attachment surface of the conductor arm,
the conductor arm being an integral flat conductive ribbon having a
first end having the attachment surface and being oriented for
attachment the attachment surface may contact the second terminal
attachment surface and a second end conductively coupled to a
remote terminal assembly for installing the circuit protection
device in a circuit to be protected, and a middle portion of the
conductor arm being coiled to bias the first end of the conductor
arm to move away from the second terminal of the voltage sensitive
device upon release of the thermal connector.
30. A circuit protection device comprising: a voltage sensitive
element having a first terminal and a second terminal, the second
terminal having an attachment surface; a conductor arm having an
attachment surface; a thermal connector releasably connecting the
attachment surface of the second terminal of the voltage sensitive
element to the attachment surface of the conductor arm, the
conductor arm being biased to move away from the second terminal
when released by the thermal connector; a second voltage sensitive
element having a first terminal and a second terminal, the second
terminal of the second voltage sensitive element having an
attachment surface; a second conductor arm having an attachment
surface; a second thermal connector releasably connecting the
attachment surface of the second terminal of the second voltage
sensitive element to the attachment surface of the second conductor
arm, the second connector arm being biased to move away from the
second terminal of the second voltage sensitive device upon release
of the thermal connector; and, both voltage sensitive elements are
connected together by a connecting structure such that their
respective conductor arms are contained in a space defined between
both voltage sensitive elements.
31. The circuit protection device of claim 30 wherein the
connecting structure is situated in a housing at least partially
surrounding the voltage sensitive devices.
32. The circuit protection device of claim 31 wherein the
connecting structure includes a first common terminal for
conductively coupling the first terminals of the voltage sensitive
devices and a second common terminal for conductively coupling the
conducting arms.
33. The circuit protection device of claim 30 including a braided
conductor connected between the conductor arm and a remote third
terminal adapted for connection to standard fixtures.
34. The circuit protection device of claim 32 including braided
conductors connecting between the conductor arms and the second
common terminal.
35. The circuit protection device of claim 30 wherein the conductor
arm is substantially flat with opposing relatively wider flat
surfaces relative to opposing relatively narrower edge surfaces, at
least one of the wider surfaces being oriented to face the voltage
sensitive device.
36. The circuit protection device of claim 30 wherein the voltage
sensitive device is an MOV and at least the second terminal is in
direct contact with the semiconductor core of the MOV.
Description
TECHNICAL FIELD
[0001] The present invention relates to overvoltage protection
devices for electrical circuits and equipment; and more
specifically, to a circuit protection device.
BACKGROUND OF THE INVENTION
[0002] Electronic protection devices such as voltage surge
protectors are commonly used to protect electric or electronic
equipment such as PLCs, computers, and entire electrical
installations against destructive overvoltage surges. Such surge
protection devices guard the electronic circuitry against
detrimental power surges generated from various sources, including,
but not limited to: motors, transformers, welding machines,
lightning strikes, and power-grid-switching by the energy supplier.
To protect against unacceptable voltage surges, voltage sensitive
devices are employed to absorb or shunt current safely away from a
circuit to be protected.
[0003] A very useful voltage sensitive device is a varistor such as
a metal oxide varistor (MOV). MOVs are solid-state surge protective
devices widely used with low-voltage AC circuits to protect
electrical devices and sensitive loads. Varistors are non-linear
electronic devices generally comprised of a ceramic compound for
example, zinc oxide (ZnO) granules doped with other
compounds--principally oxides of bismuth, cobalt, manganese,
chromium, and tin. The material is fabricated by mixing finely
powdered constituents of a binder agent. This mixture is pressed
into thin disks and then fired in an oxidizing atmosphere at around
1200.degree. C. The two faces of the disks are then coated with an
electrically conducting compound and terminals are attached by
soldering. The assembly is then coated with a thin covering of
epoxy or other insulating material to provide electrical insulation
and mechanical protection.
[0004] At nominal power system levels, a varistor presents a high
resistance to a circuit and does not conduct any significant
current. However, in a transient power surge condition, the
varistor can be utilized to limit the transient over-voltage and to
divert transient current surges away from the circuits to be
protected. The effect of the varistor can be scaled to handle
larger surge currents and energies by increasing the size of the
varistor or by connecting multiple varistors in parallel. A
varistor can be designed to limit transient voltages in circuits to
be protected to a specified level can also be designed and
configured to divert transient currents of specified current levels
and/or wave shapes.
[0005] A chief characteristic of a varistor is that over a wide
range of electrical current, the voltage drop across the varistor
remains within a narrow band commonly called the varistor voltage.
A log-log plot of the instantaneous voltage (in volts) versus the
instantaneous current (in amps) yields a nearly horizontal line.
Their current-voltage characteristics make varistors well suited
for protection of sensitive electronic circuits against electrical
surges, over-voltages, faults, and shorts. When subjected to a
voltage exceeding its voltage limit, the varistor becomes highly
conductive, absorbs and dissipates the energy related to the
over-voltage, and typically limits the current to a neutral line or
ground plane.
[0006] One significant limitation of a varistor is that during a
power surge when a varistor is conducting high currents, it will
generate heat in excess of what it can satisfactorily dissipate.
The heat is generally proportional to the area of the varistor as
well as the wave shape of the current and is a limiting factor in
the capability of the varistor to conduct current. If an
over-voltage condition is not timely discontinued, the varistor can
continue to increase in temperature and can ultimately fail, i.e.,
rupture or explode. It is possible for such a failure to destroy
nearby electronic components and equipment. The failure of a
varistor in a surge suppression system may allow the fault
condition to reach the sensitive electronic equipment the system
was designed to protect.
[0007] Others have provided structures to prevent or ameliorate the
over heating problems discussed above. For example U.S. Pat. No.
6,430,019 issued to Martenson et. al. discloses a "thermal switch"
which physically disconnects electrical connection of the voltage
sensitive device from its circuit upon an over-voltage thermal
event. However, the structures disclosed in Martenson et. al.
require a number and type of components, and arrangement of those
components, that would appear to complicate construction and
operation of the circuit protection device.
[0008] Thus, there presently is a need for a reliable and compact
mechanism to prevent thermally related failures of circuit
protection devices.
[0009] The present invention is provided to address these needs and
to provide other advantages.
SUMMARY OF THE INVENTION
[0010] Generally the invention is directed to a circuit protection
device having a voltage sensitive element (such as an MOV) that is
electrically connected in its operative circuit by a moveable
conductor arm. Upon exceeding an unacceptable temperature in the
voltage sensitive element, the conductor arm is physically moved
out of contact with a terminal connected to the voltage sensitive
element by a biasing spring so as to open the circuit of the
protection device.
[0011] According to one embodiment of the invention a circuit
protection device comprises a voltage sensitive element having a
first terminal and a second terminal. The second terminal of the
voltage sensitive element includes an attachment surface. A
conductor arm includes an attachment surface and is releasably
connected--via a thermal connector--to the voltage sensitive
element. That is, the attachment surface of the conductor arm is
releasably coupled to the attachment surface of the second terminal
of the voltage sensitive element. The connector arm is biased to
move--when released by the thermal connector--in a direction along
a line having an acute angle with respect to a plane defined by a
lateral dissection between the connected attachment surfaces, the
angle being no greater than 45.degree. on either side of the plane.
However, for among other things, optimizing space savings, the
angle of movement is optimally approximately between 0.degree. and
10.degree., but more optimally between 0.degree. and 5.degree., on
either side of the plane. The first and second terminals and the
attachment surfaces can be oriented with respect to the main body
of the voltage sensitive device such that this proscribed motion
will provide a reliable and compact component for a circuit
protection device. This is particularly advantageous when the
movement coincides with the conductive arm moving laterally along a
face of a disc-shaped varistor.
[0012] According to another embodiment of the invention, a spring
is directly connected between the conductor arm and a support
structure of the circuit protection device. The spring biases the
conductor arm to move the conductor arm upon release of the
conductor arm from a terminal connected to the voltage sensitive
element. In one embodiment the spring is in axial tension when the
conductor arm is connected to the second terminal and retracts to
move the conductor arm upon its release from the second terminal of
the voltage sensitive device. In alternate embodiments the spring
is configured to be in torsional stress when the conductor arm is
connected to the second terminal of the voltage sensitive element
and relaxes the stress to move the conductor arm upon its release
from the second terminal.
[0013] In an embodiment of the invention, the voltage sensitive
element is a varistor, such as a metal oxide varistor and the
thermal connector is a low-temperature solder which liquefies at a
temperature between 114-124.degree. C.
[0014] In another embodiment of the invention, the above-mentioned
circuit protection devices may include a second voltage sensitive
element and a second conductor arm. The conductor arms are both
situated in a space defined between the two voltage sensitive
elements. Due to the shape of the conductor arms and the direction
of their movement upon release, the two voltage sensitive elements
can be packaged relatively closely to each other in a single
package with a relatively smaller footprint
[0015] Yet another embodiment of the present invention provides a
circuit protection device including a voltage sensitive element
having a first terminal and a second terminal; the second terminal
further having an attachment surface. A thermal conductor
releasably attaches an attachment surface of a conductor arm to the
attachment surface of the second terminal of the voltage sensitive
element. The conductor arm is biased by a spring held in torsional
stress wherein the spring as it relaxes moves the conductor arm
away from the second terminal of the voltage sensitive device upon
release of the thermal connector. In an alternative embodiment the
conductor arm is biased by a spring which is directly connected
between the conductor arm and a support structure. The spring is
held in axial tension.
[0016] In an embodiment of the invention, a circuit protection
device includes a moveable conductor arm being connected to a
terminal remote from the voltage sensitive device by a flexible
conductor such as a braided or twisted wire cable.
[0017] In an embodiment of the circuit protection device of the
invention, a moveable conductor arm comprises an integral flat
conductive ribbon having a first end having an attachment surface
oriented for attachment to the attachment surface of a voltage
sensitive element and having a second end conductively coupled to a
remote terminal used for connecting the circuit protection device
to a circuit to be protected. A middle portion of the conductor arm
is coiled to provide bias to the first end of the conductor arm so
as to move it away from the second terminal of the voltage
sensitive element upon release of a thermal connector.
[0018] One object of the present invention is to provide a compact
and reliable circuit protection device which is less susceptible to
a failure caused by excessive heat generated by a voltage sensitive
device such as a varistor.
[0019] Other advantages and aspects of the present invention will
become apparent upon reading the following description of the
drawings and detailed description of the invention.
DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective of one embodiment of the present
invention with a voltage sensitive element mounted in a housing
with a conductor arm conductively attached to the voltage sensitive
element;
[0021] FIG. 2 is a perspective view of the embodiment of FIG. 1
with the conductor arm released from the second terminal of the
voltage sensitive element;
[0022] FIG. 3 is a front view of the embodiment of FIG. 1;
[0023] FIG. 4 is a plan view of one embodiment of the voltage
sensitive element of the present invention;
[0024] FIG. 5 is a is a cross-sectional front view of the voltage
sensitive element shown in FIG. 4;
[0025] FIG. 6 is a schematic cross-sectional view of the embodiment
of FIG. 1 depicting relative movement between the conductor arm and
the voltage sensitive element;
[0026] FIG. 7 is a schematic view of an alternate embodiment of the
present invention depicting an alternate shape of the second
terminal and relative movement between the attachment surface of
the conductor arm and the second terminal;
[0027] FIG. 8 is a schematic view of an alternate embodiment of the
second terminal of the present invention depicting relative
movement between the conductor arm attachment surface and the
attachment surface of the second terminal;
[0028] FIG. 9 is a front view of an alternate embodiment of the
present invention with the voltage sensitive element mounted in a
housing with the conductor arm conductively attached to a
conductive contact defining the second terminal;
[0029] FIG. 10 is front view of the embodiment of FIG. 9 with the
conductor arm released from the conductive contact;
[0030] FIG. 11 is a schematic cross-sectional side view of the
conductive contact connected to the voltage sensitive element;
[0031] FIG. 12 is a front view of another embodiment of the present
invention with two voltage sensitive elements within a single
housing;
[0032] FIG. 13 is a cross-sectional view of the embodiment of FIG.
12 taken along line 13-13 of FIG. 12;
[0033] FIG. 14 is an exploded view of the embodiment of FIGS. 12
and 13;
[0034] FIG. 15 is a schematic diagram of the present invention
depicting an alternate embodiment of the conductor arm and biasing
spring; and,
[0035] FIG. 16 is a schematic diagram of the present invention
depicting an alternate embodiment of the conductor arm and biasing
spring.
DETAILED DESCRIPTION OF THE INVENTION
[0036] While the present invention is capable of embodiment in many
different forms, there is shown in the drawings and will herein be
described in detail exemplary embodiments of the invention with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the broad aspect of the invention to the
embodiments illustrated. Like parts used in the various embodiments
disclosed may use the same reference numbers unless otherwise
stated.
[0037] FIGS. 1-6 disclose a circuit protection device 10 according
to one embodiment of the invention. The circuit protection device
10 includes a voltage sensitive element 12, a conductor arm 20, a
thermal connector 24, a spring 28, a first common terminal 25, a
second common terminal 30 (see also FIG. 14), a housing 23, and
terminals 15 and 17 extending from the housing for connecting the
circuit protection device 10 to a circuit to be protected.
[0038] FIGS. 4 and 5 disclose that the voltage sensitive device 12
is in the form of a metal-oxide varistor (also referred to herein
as "MOV 12" or "varistor 12"). The MOV 12 can be comprised for
example, of a semiconductor material 11 which can include zinc
oxide granules. The material 11 is sandwiched between conductive
plates 14a and 16a. The plate 14a has a blade or tab-type extension
forming a first terminal 14 of the MOV 12 while in this instance
the conductive plate 16a defines a second terminal 16 for
electrically connecting to the MOV 12.
[0039] In other embodiments, for example those terminals
schematically disclosed in FIGS. 7 and 8, the second terminal 16
could be in any useful shape or form for electrical connection to
the plate 16a, including a tab or blade-type terminal. However, in
the circuit protection device 10, employing plate 16a (more
particularly an attachment surface 18 on the plate 16a) as the
second terminal 16 has the advantage of increasing the sensitivity
to thermal events in the MOV 12.
[0040] FIGS. 1-3 disclose a conductor arm 20 which is electrically
connected between the MOV 12 and terminal 17. As better disclosed
in FIG. 6, the conductor arm 20 has an attachment surface 22. FIGS.
5 and 6 disclose that the attachment surface 22 is releasably
attached to the attachment surface 18 of the second terminal 16 of
the MOV 12 by the thermal connector 24. The thermal connector 24
can be selected to release (in this case liquefy) at any desired
temperature depending on the desired tolerance for heat build up in
the MOV 12. For example, a low-temperature solder bump is capable
of operably coupling the attachment surface 22 of the conductor arm
20 with the attachment surface 18 of the second terminal 16. The
low-temperature solder 24 can be chosen to liquefy well below the
temperature required to melt conventional solder connections, i.e.
183.degree. C. For example there are solders available which
liquefy at between 114-124.degree. C.
[0041] FIGS. 1 and 2 disclose that the conductor arm 20 is biased
by spring 28 to move when released by liquefaction of the thermal
connector 24. As further disclosed in FIG. 6, the direction of
movement is in a direction along a line (indicated by the arrow in
FIG. 6) having an angle a with respect to a plane 26 defined by a
lateral dissection (indicated by line L-L of FIG. 6) between the
connected attachment surfaces 18 and 22. Referring again to FIG. 6,
the angle a is not greater than 45.degree.--and is optimally
between 0.degree. (parallel) and 10.degree.--or 0.degree. to
5.degree. on either side of the plane 26.
[0042] Referring back to FIGS. 1-3, and to FIG. 14, it can be seen
that the conductor arm 20 is biased by spring 28. In this
embodiment, the spring 28 may or may not be conductive. One end of
spring 28 is operably connected to the conductor arm 20 and the
other end is connected to a common terminal plate 30 which is in
turn integrally connected to terminal 17. The spring 28 can be
connected to the common terminal plate 30 through a variety of
means however, as is shown in FIGS. 3 and 14 one end of the spring
28 resides within a tubular spring holder 38 formed from the same
piece of metal as the common terminal plate 30. The helix of the
spring 28 is secured by a spring pin 32 of housing 23. In this
configuration, when positioned as shown in FIGS. 1 and 3, the
spring 28 is placed in torsional stress to bias the conductor arm
20.
[0043] FIG. 2 depicts the circuit protection device 10 after the
MOV 12 has heated to the point of liquefying the thermal connector
24 and thereby releasing the conductor arm 20, thus enabling it to
move laterally and off to the side--generally parallel with the
plane 26 defined by a lateral dissection between the connected
attachment surfaces 18 and 22. As can be seen in FIG. 2, the
contact surface 22 of conducting arm 20 has moved after a
triggering thermal event in the MOV 12, to a safe position well
away from the second terminal 16 and is nearby only to the housing
23 which is a non-conductive plastic and to the insulating material
on a remote portion of the MOV 12. This ending distance and
location are meant to prevent incidental conduction with carbon or
solder trails which may form upon a pre-or-post excessive thermal
event.
[0044] The conductor arm 20 is electrically connected to the common
terminal 30 by a flexible conductor such as a braided or twisted
wire cable 48. This flexibility accommodates the distance moved by
the conductor arm during assembly and after a release from
attachment to the second terminal of the MOV 12.
[0045] The first common terminal 25 accepts MOV 12 tab terminal 14
into a slot therein. The common terminal is mounted within the
housing 23 for this purpose and for structurally stabilizing the
MOV 12 while providing at its distal end the terminal 15 for
connecting to a circuit to be protected.
[0046] FIGS. 7 and 8 disclose schematically the beneficial movement
of a conductor arm according to the invention on second terminal
types of different from the second terminal 16. In particular FIGS.
7 and 8 disclose in schematic cross sectional views, two
differently shaped terminals 27 and 29 respectively which are
connected with low-temperature solder to two different attachment
surfaces on moveable conductor arms such as conducting arm 20 (FIG.
7) and a conducting arm 31 respectively. As can be seen by the
lines L-L in both FIGS. 7 and 8, and the arrows showing movement,
the movement is in a line parallel (.alpha.=0.degree.) with the
plane 26 dissecting the attachment surfaces between the attachment
points of the terminals 27, 29 and the conductor arms 20 and 31. In
other words, benefits according to the invention can be obtained
for the relative movement of the attachment surfaces of the
conductor arms 20, 31 and the attachment surfaces of the terminals
away from each other in a lateral direction even where the
terminals are more remote from the voltage sensitive element and
where the attachment surfaces are shaped other than flat.
[0047] Another embodiment of the present invention is shown in
FIGS. 9-11 wherein a conductive contact, or terminal pad 40 is
utilized to facilitate initial lateral movement of the conductor
arm 20. More specifically as disclosed in FIG. 11, the MOV 12 has a
non-conductive material 42, e.g., epoxy or other insulating
material, which substantially encases the MOV 12. A portion of the
second plate 16a forming the second terminal 16 remains exposed but
presents a lip or edge in the coating which could impede the
movement of the conducting arm 20. Thus the terminal pad 40 is
coupled to the exposed portion of the second terminal 16 to offset
the attachment surface 18. As shown in FIG. 11, the terminal pad 40
is positioned to extend a distance beyond the non-conductive
material 42. The conductor 20 in this embodiment is releasably
attached to the terminal pad 40 (now defining a second terminal) at
attachment surface 22 by thermal connector 24. In this
configuration, upon initial movement of the conductor arm 20 away
from the terminal pad 40, the arm is prevented from snagging on an
edge of the coating 42 or other obstacles surrounding the
dielectric coating in that area.
[0048] FIGS. 9 and 10 disclose an auxiliary insulating sheet 44
which may also be used with the circuit protection device 10. The
sheet 44 of dielectric material, e.g., mica, has an opening 43
disposed proximate the second terminal 16 of the MOV 12 and the
opening 43 is sized relative to the terminal pad 40 such that a
portion of the sheet 44 lies between the MOV 12 and the conductive
contact 40. This configuration helps to secure the insulating sheet
44 while also preventing an edge of its opening 43 from obstructing
movement of the conductor arm 20. It should also be noted that
canted edges 20a and 20b (see e.g. FIGS. 3 and 11) on the conductor
arm 20 also provide assistance in avoiding obstruction by
irregularities in the structures within the path of conductor arm
20 when it moves.
[0049] FIGS. 12-14 show configurations of an alternative embodiment
of the present invention wherein multiple--optimally two--MOV 12
are configured within the housing 23. A second MOV 112 has a first
terminal 114 and a second terminal 116. The second terminal 16 of
the second MOV 112 has an attachment surface 118. A second
conductor arm 120 includes an attachment surface 122 wherein a
second thermal connector 124 releasably connects the attachment
surface 118 of the second terminal 116 of the second MOV 112 to the
attachment surface 122 of the second conductor arm 120. The second
conudctor arm 120 is biased to move in a direction generally
parallel with a second plane 126 defined by a second lateral
dissection between the connected attachment surfaces 118, 122 of
the second MOV 112 and the second conductor arm 120.
[0050] FIGS. 12-14 disclose various connecting structures for
providing proper orientation of the MOVs 12, 112 and the conductor
arms 20, 120, for securing them in the housing 23 and for providing
conductive pathways for connecting the MOVs to a circuit to be
protected. In particular, as disclosed in FIG. 13, the MOVs 12, 112
are connected together by connecting structure such that their
respective conductor arms 20, 120 are contained in a space 50
defined between both MOVs 12 and 112.
[0051] Connecting structure may include the first common terminal
25 which accepts the terminals 14 and 114 from the respective MOVs
12 and 112 in slots formed in an upper portion of the common
terminal 25. The common terminal 25 also fits into and cooperates
with internal structure of the housing 23 in a way 50 as to assist
secure placement and alignment of the MOVs 12 and 112 while also
providing electrical connectivity through remote terminal 15 to a
circuit to be protected. Similarly, the common terminal 30 is also
adapted to secure a second spring 128 in a tubular connector 38 for
biasing the conductor arm 120 while providing electrical
connectivity for both conductor arms 20, 120 through remote
terminal 17 to a circuit to be protected. The common terminal plate
30 also fits into and cooperates with the housing 23 in a way to
secure proper orientation and spacing of the conductor arms 20, 120
with respect to their respective MOVs 12 and 112. A removable bulk
head 52 in cooperation with a snap-lock connector 54 assists in
providing a stable and secure seat for the fully-assembled
structures in housing 23. The helical coil of both springs 28 and
128 are secured on spring pin 32 the unsecured end of which becomes
capped and secured by the snap-lock connector 54.
[0052] FIG. 14 discloses that the second conductor arm 120 is also
conductively connected to the second common terminal 30 via
flexible conductor 148 in the form of a braided or twisted wire
cable 148. In this duplex embodiment, the flexible connectors 48
and 148 may be made separately or can be formed from a single cable
which is connected near its center to the common terminal 30.
[0053] It should be appreciated, in particular in view of FIG. 13,
that the above-disclosed arrangements provide for a compact circuit
protection device with a "foot print" which is advantageous for use
in product designs where component space is at a premium.
[0054] For example, according to one aspect of the invention,
arranging to have both moveable arms in the shared space 50, by
itself permits space savings. In addition to that, the path of
travel for the conductor arms 20, 120 provides a tight operational
profile enhancing the ability to package the MOVs 20 and 120 closer
together. In addition to that, it should be appreciated that the
conductor arms 20 and 120 are substantially flat with opposing
relatively wider flat surfaces compared to the relatively narrower
opposing edge surfaces. This permits a wider surface to be oriented
to face the attachment surfaces 18 and 118 for connection while
aiding in space saving when the MOVs are spaced side-by-side as
disclosed in FIG. 13.
[0055] It should also be appreciated that the conductor arm and
spring assemblies disclosed the circuit protection devices of the
present invention have advantages in terms of reliability and a
relatively low part-count.
[0056] FIG. 15 discloses in a schematic way, an alternative
embodiment of a conductor arm 56 which may be used according to the
invention. In particular, an integral flat conductive ribbon 58 is
provided for releasable connection between the second terminal 16
of MOV 12 and a remote terminal 60 used for connecting the circuit
protection device to a circuit to be protected. Thermal connector
24 (e.g. solder) is used for the temperature sensitive connector to
join a first end 62 of the spring 60 to second terminal 16 of MOV
12 as described above. A second end 64 of the conductive ribbon 58
is conductively coupled to the remote terminal 60. A middle portion
66 of the ribbon 58 is coiled so as to bias the first end 62 of the
conductor arm to move away in the direction of the arrow in FIG.
16, from the terminal 16 of the MOV 12 upon release by the thermal
connector 24.
[0057] FIG. 16 discloses in a schematic way, an alternative
embodiment of a conductor arm 68 according to the invention. The
conductor arm 68 has a first end 70 releasably attached to the
second terminal 16 of the MOV 12 by a thermal connector 24, while a
second end 72 of the conductor arm 68 is conductively coupled with
a remote terminal 74 by a flexible cable 76, such as a braided
cable or a twisted wire bundle. End 72 of the conductor arm 68 is
also pivotally connected to support structure (not shown) within
the housing 23 by a pin 78 e.g. a rivet or the like. A spring 80 is
directly connected between the conductor arm 68 and support
structure (not shown) such as may be made available in a housing
like housing 23 or other structures accommodating an anchoring
point for one end of spring 80. As depicted in FIG. 16, the spring
82 is in axial tension while the conductor arm 70 is attached to
the second terminal 16 of the MOV 12. Upon release of the end 70 of
the conductor arm 68 by the thermal connector 24, the spring 82
will move the conductor arm 70 about its pivot in the direction of
the arrow shown in FIG. 16. Optimally for compact packaging of this
schematic embodiment, the conductor arm 68 will move in a direction
along a line having an acute angle with respect to a plane defined
by a lateral dissection between the connected attachment surfaces,
the angle being no greater than 45.degree. on either side of the
plane. Optimally the angle .alpha. of movement is approximately
between 0.degree. and 10.degree., but more optimally between
0.degree. and 5.degree., on either side of the plane.
[0058] While specific embodiments of the present invention have
been illustrated and described numerous modifications come to mind
without significantly departing from the spirit of the invention
and the scope of protection is only limited by the scope of the
accompanying claims.
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